Shunt regulator circuits are used in ICs, for example, in the active ORing IC part number IR5001 made by International Rectifier Corporation of El Segundo, Calif.
FIG. 1 is a diagram of a circuit employing the IR5001 IC. The ICs actively OR two 48 volt power supplies by controlling the power FETs. A shunt-regulator (FIG. 2) is used to draw a variable current through a resistor R that is connected at one terminal to the line voltage VLINE, so as to maintain a regulated voltage VCC at the other terminal of the resistor. This terminal of the resistor thus serves as the regulated power-supply of the IC. It is also the output of the shunt-regulator and is labeled as the VCC pin of the IC.
In the previous IC (IR5001), there is a maximum limit on the resistor value so that the current drawn from the minimum line voltage is able to operate the IC, otherwise, a resistor external to the IC has to be used. However, at maximum line voltage, the power-dissipation of an internal resistor generates thermal dissipation that is unacceptable to the present IC package. Thermal runaway will reduce the reliability of High-voltage ICs.
Previous method of using a fixed-value internal resistor for shunt regulation, as in IR5001, is not efficient. The solution in IR5001 requires an external resistor to be chosen for different line voltage if the fixed-value internal resistor is not appropriate. In addition, the reliability of the previous method is inadequate when the resistor is subjected to voltages above the device's operational rating.
Known prior art includes:    1. U.S. Pat. No. 3,535,613: “Compensated Solid State Voltage Regulator Circuit Including Transistors and Zener Diode.”    2. U.S. Pat. No. 3,648,153: “Reference Voltage Source.”    3. U.S. Pat. No. 3,851,241: “Temperature Dependent Voltage Reference Circuit.”    4. U.S. Pat. No. 4,103,219: “Shunt Voltage Regulator.”    5. IR5001 data sheet and application of the internal shunt-regulator.
In addition to power-dissipation and thermal reliability issues, the invention provides a novel solution to high-voltage biasing, despite the limitation in International Rectifier's Gen 5 technology for 22V-rated devices. The resistors in Gen 5 are rated at 22V and would not be able to operate reliably at a line voltage of 100V.
The Gen 5 technology referred to above refers to the technology for the manufacture of high voltage PMOS devices as at least partly disclosed in the following patents:    1. U.S. Pat. No. 5,861,657: “Graded Concentration Epitaxial Substrate for semiconductor device having resurf diffusion.    2. U.S. Pat. No. 5,686,754: “Polysilicon Field Ring Structure for Power IC.”    3. U.S. Pat. No. 5,801,418: “High Voltage Power Integrated Circuit with Level Shift Operation and Without Metal Crossover.”    4. U.S. Pat. No. 5,801,431: “MOSgated Semiconductor Device with Source Metal Covering the Active Gate.”